There are already known a number of planar patch antennas the bandwidth of which one has been trying to widen for a long time, in order to allow receiving waves in a broad frequency band by means of one and the same antenna.
In this respect, it should be noted that the terrestrial television signals, whether they are digital and/or analogue, have a frequency varying between about 470 and 870 MHz. As a matter of fact, unless extremely complex technical means were implemented, prior to the invention, this frequency band could not be covered by means of one and the same planar patch antenna.
In particular, as regards the planar patch antenna, there is known one that is comprised of a simple planar reflector made out of conductive material above which extends, separated by a dielectric substrate, a radiator in the form of a conductive plate the dimensions of which are determined so as to allow it, under the action of a specific current supply, to radiate at a determined frequency.
If the reflector has increased dimensions compared to the radiator, it is intended to widen the bandwidth of the antenna downwards. More exactly, this reflector is tuned, through its strip line coupling to the radiator, to a low frequency, i.e. lower than the radiation frequency of the radiator.
In order to widen the bandwidth upwards, there has been devised to superimpose to the radiator non-fed parasitic planar conductive elements. Through their stripline coupling to the radiator, these parasitic elements are caused to radiate in the upper portion of the bandwidth.
In a more recent design, there has been carried out a patch antenna the radiator plate of which, fed by a specific feeder, is tuned to a first frequency, taking into consideration that in this plate is cut out a U-shaped slot of constant width which resonates at a different frequency.
Obviously, when coupled at the radiation frequency of the radiator, this antenna with a slot results into widening the bandwidth.
The U-shaped configuration of the slot and its symmetrical arrangement with respect to the median plane transversal to the radiator, as well as the current supply occurring in this transverse plane, have been considered essential parameters to allow the electromagnetic current-supply to this slot.
In brief, a simple rectilinear slot provided in this radiator cannot be subjected to an electromagnetic current under the action of a feeder simply connected to the radiator.
Obviously, such a U-shaped slot of constant width can only radiate on its basic resonance.
To conclude, the solutions adopted hitherto have allowed a widening of the bandwidth of a patch antenna in the range of 20 to 40%, compared to its basic radiation frequency, this, of course, for a reception with a sufficient gain to allow using the received signal.
From US-2002/003499 is also known an antenna with a conductive layer and a two-band transmission device including this antenna. The latter includes a dielectric substrate including, on its lower and a higher faces, a conductive layer, the first one forming a mass, the reflector, and the second one forming a patch, the radiator, both being connected, here, by a short-circuit strip extending on a surface of a slice of the substrate.
In this case, the antenna also includes a coupling system including a primary strip line coupling formed by two slots extending parallel to each other in the wafer and forming two primary coupling slots, respectively, while a secondary strip line coupling formed by a third slot is connected to one of its two primary coupling slots.
The patch also includes a separating unit including at least a separating slot so as to create two zones forming a primary resonance zone and a secondary resonance zone, respectively. In fact, according to a particular embodiment described in this document, the separating unit can be defined by a U-shaped separating slot, remaining at a distance from the edges of the wafer and including two legs connected to each other by a base.
It should be noted, in particular, that the width of each of the separating slots forming the U is the same, while the parallel outermost slots include a similar length.
As set forth in this former document, the coupling between, on the one hand, the standing wave of each of both primary and secondary resonances and, on the other hand, the waves radiated in space, mainly occurs on one or several edges of the patch or of the separating slots or through these slots. It is specified that, in the embodiment including a U-shaped separating slot, the connecting slot forms a secondary radiating slot in addition to the other two parallel slots.